When Ambrosio was 12 years old, she enrolled in modeling classes then, began modeling for Dilson Stein at age 15. Winning Brazil's Elite Model Look started her modeling career. Her first big modeling job was the cover of the Brazilian Elle magazine. Elite passed along some of her Polaroids to Guess which led her to do the Millennium GUESS? campaign along with her friend and fellow Brazilian Ana Beatriz Barros. She has since been in huge demand, working with big-name brands including Revlon, Christian Dior, Giorgio Armani, Rolex, Oscar de la Renta, Gucci, Escada, Rocco Barocco, Calvin Klein and Ralph Lauren, as well as the famed Pirelli Calendar. As for fashion shows, she has walked the catwalks for designers such as Laura Biagiotti, Christian Lacroix, Byblos, Fendi, Issey Miyake, Kenzo, Christian Dior, Nicole Miller, Ralph Lauren, Giorgio Armani, Vivienne Westwood, Oscar de la Renta, among others. She appeared in over 50 international magazine covers such as Cosmopolitan, Elle, GQ, Harper's Bazaar, Marie Claire, Ocean Drive, Vogue and the only model to appear on the cover of Glamour in the United States in 2006.

In 2004, Ambrosio launched her line of swimwear called Alessandra Ambrosio by Sais, a division of Rosa Chá. It sold 10,000 units in only its first month on the market. Since then, not much has been said about the constant growth of the line, but I am sure with her modeling assests, boyfriends everywhere are getting their girlfriends these suits for the upcoming holidays.

Her best knowns collaboration is with American lingerie brand Victoria's Secret. She appeared in the Victoria's Secret Fashion Show for the first time in 2000, and continues to be a participant in the subsequent shows. Her most notable walk down the runway was in 2005 wearing lingerie made entirely out of candy. In 2004, she was selected as the first spokesmodel for Victoria's Secret PINK line. She is currently a contract 'Angel' and spokesmodel for Victoria's Secret. Her 'Angel' status has brought her to the public's attention being cited by the popular media as one of the world's sexiest women. She was chosen as one of People magazine's annual 100 Most Beautiful People in the World, in May 2007 along with fellow 'Angels' Ambrosio is among the world's top-earning models.

• "Entourage" .... Victoria Secret's Angel (1 episode, 2007)
       - Less Than 30 (2007) TV episode .... Victoria Secret's Angel
• Casino Royale (2006) .... Tennis Girl
  ... aka James Bond 007 - Casino Royale (Germany)
• Victoria's Secret Fashion Show (2008) (TV) .... Herself
• The Victoria's Secret Fashion Show (2007) (TV) .... Herself/Model
• "How I Met Your Mother" .... Herself (1 episode, 2007)
       - The Yips (2007) TV episode .... Herself
• The Victoria's Secret Fashion Show (2006) (TV) .... Herself/Model
• "Late Night with Conan O'Brien" .... Herself (1 episode, 2006)
  ... aka Late Night with Conan O'Brien (Australia)
       - Episode dated 16 October 2006 (2006) TV episode .... Herself
• "The Tyra Banks Show" .... Herself (2 episodes, 2005-2006)
       - Model Madness (2006) TV episode .... Herself
       - Secrets of the Supermodels (2005) TV episode .... Herself